Water and hydrate management is a known challenge in subsea gas developments. Hydrates are formations of ice and gas that may form due to high pressures and low temperatures in hydrocarbon extraction environments. These hydrates may then clog the production systems, leading to hazardous conditions. Many subsea gas wells produce no to very little formation water at start-up. The gas in the reservoir is (nearly) always saturated with water vapor. At the wellhead or other location within the gas production system, some of the water vapor may have condensed and may be present as condensed or de-ionized water. If so, there will still be water in the vapor phase in the gas at the wellhead and throughout the production system, and thus further condensation of water may occur downstream of the wellhead.
Gas reservoirs might contain salty, interstitial water in the source rock, or may be connected to aquifers containing salty formation water. However, it may be desirable for a well operator to continue producing gas from a well even after that well has started to produce such formation water. The volumetric fraction of formation water in the production fluid is usually very small, for example less than about 1% of the total volume, making it difficult to accurately measure the production rate of formation water. To complicate things further, the formation water and the condensed water might mix as water is condensing out of the gas vapor phase in the wellbore, at the wellhead, and/or further downstream in the production system.
In some installations, a measurement device such as a multiphase or wet gas meter may be located at or near the wellhead to measure the production rates of gas, gas condensate, and water. The total water fraction being small, the associated measurement uncertainty is correspondingly large to the point of significantly impairing the accuracy of such measurement. For example, a wet gas meter may have a water volume fraction measurement uncertainty of 0.1%, while the actual liquid water volume fraction might be 0.05% (500 ppm).